Shuttle Discovery on the launch pad Monday

KENNEDY SPACE CENTER, Florida (CNN) -- NASA operations managers were to decide later Monday whether to go ahead with Tuesday's scheduled launch of the U.S. space shuttle Discovery on a mission to bring back U.S. astronaut Andy Thomas.

The mission could be delayed because of computer problems aboard the Russian space station Mir, where Thomas has lived for the last four and a half months.

As of Monday morning, the countdown for tomorrow's launch was under way for the scheduled 6:10 p.m. EDT launch, NASA officials said Monday.

Earlier in the day, ground specialists and the Mir crew successfully restarted the main onboard computer of Mir, two days after it failed, Russian mission control said.

"The cosmonauts are now loading software into the station's computer. It underwent tests after being rebooted earlier and it looks like everything is working fine," a spokeswoman said by telephone from Korolyov, outside Moscow.

The computer, which controls the station's orbital alignment, failed on Saturday, leaving Mir adrift but in no immediate danger.

Attempts to restart the troublesome computer on Sunday were unsuccessful. It was replaced with a spare one, which failed to boot properly on the first try Sunday night.

Now, with computer up and running, the cosmonauts will try to re-establish alignment with the help of electrically powered gyroscopic devices and Mir's engines.

Mir

Normal alignment must be restored before the U.S. space shuttle's last visit to the Russian station to go ahead as planned. NASA's flight rules require Mir to have a working control system before the space shuttle can dock.

On Sunday, Thomas, 46, told NASA officials he was nervous that Mir's computer problems could delay his return to Earth.

Thomas told Scott Gahring, head of operations for NASA at Russian Mission Control, that he wants the shuttle to come and get him as soon as possible.

"He's a little nervous, but no more so than I think anybody would be when your ride looks like it could be (affected)," Gahring said. "He's doing pretty good."

Reuters contributed to this report.

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